1. Field of the Invention
The present invention relates to semiconductor processing and, more particularly, to planarizing the surface of a semiconductor wafer or device during manufacture. Specifically, one embodiment of the present invention provides a method in which dependencies of polish rate and post-polish substrate thickness on process parameters of downforce, polish pad spring constant and polish speed, and on product characteristics of high feature area on the wafer, low feature area on the wafer, pre-polish thickness of high feature areas on the wafer, and pre-polish thickness of low features on the wafer, are explicitly defined and used to control Chemical-Mechanical Polish in Run-to-Run and real-time semiconductor production control applications.
2. Description of the Prior Art
Chemical-Mechanical Polish (CMP) is an important process in microelectronic manufacturing. In this process, a silicon wafer with topographic variation on the wafer surface is polished with sufficient material removal that the wafer surface is effectively planarized, i.e., treated to have a substantially flat surface. Generally, the density, height, and geometric form of the topographic variation on the wafer surface is specific to the product and manufacturing process used by the manufacturer.
Known CMP tools, such as the Applied Materials Mirra, polish by forcing the uneven wafer surface into contact with an abrasive polish pad that is in motion with respect to the wafer surface. Typically, this motion is produced by rotation of a platen on which the pad is mounted. The platen is usually several times larger than the wafer. In addition to platen rotation, the wafer itself rotates about its center point. An alternative to this typical configuration is the Lam Research polish tool, which uses a circulating belt, rather than a rotating platen, to polish a wafer.
All known CMP tools distribute a liquid slurry across the polish pad. This slurry provides both an abrasive mechanical, as well as reactive chemical, effect that removes material from the wafer surface.
An additional aspect of polish tools is the conditioning of the polish pad between wafer polishes. This conditioning typically involves an abrasive or cutting element, such as a diamond wheel, which works across the pad surface to restore the roughness of the pad.
Often, planar wafers (that is, wafers without any appreciable surface topography) are polished in order to measure the gross removal rate of the polish tool. Typically, this action is performed after a maintenance event to qualify the tool for standard production wafers. The polish of these non-production wafers represents a cost overhead burden to the manufacturer and is minimized as much as possible.
Another technique used to quality a polish tool after a maintenance event is polishing a sample wafer or wafers from a production lot. The pre- and post-polish measurements can then be used to calculate an effective tool polish rate, and the polish time or other recipe variables are adjusted such that the bulk of the lot achieves the targeted post-polish substrate film thickness. This method also carries a cost overhead burden for the manufacturer, since the “send-ahead” sample wafer(s) are usually under-polished. Underpolished wafers can receive a second polish, termed a “rework,” to bring them to required specification; in contrast, over-polished wafers are scrapped. Reworking wafers, while avoiding scrapping of product, nonetheless carries a cost in specialized engineering attention to tailor the polish recipe to the particular requirements of the rework wafers at hand, and additionally prevents the polish tool from running normal production wafers.
Batch control schemes, termed “Run-to-Run” (R2R) control in semiconductor manufacturing, use pre-process measurements as feed forward information and post-process measurements as feedback information in conjunction with a control model to make updates to the operating recipe of the process. Standard implementations of R2R control as applied to the CMP process typically employ a simple linear model that relates polish time to the amount of material removal.